Electronic theory of ordering and segregation in transition-metal alloys

A model for the electronic energy of alloys with arbitrary composition and short-range order is applied to $4d$ transition metals. The model is not ab initio, but only requires information about pure elemental properties which is readily available. A model Hamiltonian for the alloy is derived from these elemental properties. The electronic density of states and heat of formation are calculated from the Hamiltonian with the alloy cluster-Bethe-lattice method. Charge transfer is treated self-consistently. Results for the twenty-eight $4d$ transition-metal alloys are compared to experiment and other calculations. Predictions for the stable phase at zero temperature are in excellent agreement with experiment. The model calculation allows us to examine the physical basis for experimental trends.